1. Field of the Invention
The present invention relates to a method for the preparation of metal oxide doped cerium oxide. Further, the present invention relates to such method in which the metal oxide doped cerium oxide or a complex composed of the metal oxide solid doped cerium oxide is coated with another metal oxide or blended with a compatabilizing agent for a cosmetic composition.
2. Description of the Prior Art
As is well known, ultraviolet rays cause degradation of plastic resins, and many kinds of countermeasures are carried out to protect against such degradation. As one countermeasure method, it is widely practiced that a plastic resin is admixed with an ultraviolet shielding agent including an organic ultra-violet ray absorbing agent or an inorganic ultraviolet ray scattering agent. By admixing these agents in plastic resin, the adverse influence of ultraviolet rays is reduced. As the organic ultraviolet ray absorbing agent, salicylic acid type compound, benzophenone type compound, benzotriazole type compound or cyanoacrylate type compound can be mentioned, however, recently, the lack of heat resistance, lack of durability to weather or the safety of decomposed chemicals of these compounds are becoming serious problems. To solve these problems, fine particles of titanium dioxide or fine particles of zinc oxide, which are inorganic ultraviolet ray scattering agents, are developed, however, the lack of dispersability of these agents is a problem and the catalytic activity of these agents are becoming a new problem. Recently, especially regarding titanium dioxide, it is pointed out that the generation of singlet oxygen by its photo catalyst function is causing a new problem.
Ultraviolet rays have an adverse influence also on living bodies. Namely, it is well-known that the so called UV-B ultraviolet ray in the wavelength range of 280 to 320 nm causes cutaneous inflammations such as erythematous blister and the like while the so called UV-A ultraviolet ray in the wavelength range 320 to 400 nm causes tanning of skin by the accelerated formation of melanin. As the countermeasure method against above mentioned adverse influences of the ultraviolet rays, many kinds of sunscreen cosmetic compositions have been developed heretofore. The ultraviolet shielding agents contained in conventional sunscreen cosmetic compositions can be grossly classified into two types including an ultraviolet absorbing agent such as cinnamic acid type, benzopheno ne type or dibenzoylmethane type and an ultraviolet scattering agent such as zinc oxide or titanium dioxide. However, above mentioned ultraviolet absorbing agents have several problems, such as low absorptivity of ultraviolet rays and safety when the admixing amount in a cosmetic composition is too high. Further, in a case of conventional ultraviolet scattering agent, since it is impossible to improve the transparency even if the dispersibility of particles is improved, the admixing use of it not only causes the deterioration of feeling when the cosmetic composition is applied but also the skin look becomes unnatural. Recently, the use of cerium compound as an ultraviolet scattering agent has been proposed, for example, in Japanese Patent Laid Open Publication 6-145645 or Japanese Patent Laid Open Publication 7-207151. However, since cerium oxide has strong catalytic activity, it has a problem that it accelerates the oxidation decomposition of resin or oil and causes color change and generates offensive odor when admixed in cosmetic compound or resin. Thereupon, the development of new cerium compound which has a function as the ultraviolet scattering agent and does not have catalytic activity has been desired. In Japanese Patent Laid Open Publication 9-118610, silica-cerium oxide composite particle is proposed, however, the reduction of catalytic activity of the silica-cerium oxide composite particle is almost accomplished but the ability for ultraviolet ray shielding is not sufficient.
The present invention addresses the above mentioned circumstance, to provide metal oxide doped cerium oxide with strong ultraviolet ray shielding ability, lower catalytic activity and with excellent transparency. Further, this invention provides a composite composition of metal oxide doped cerium oxide coated with metal oxide. Furthermore, this invention also provides a resin composition and a cosmetic composition in which the metal oxide doped cerium oxide or a composite thereof is admixed.
The present invention provides cerium oxide doped with metal ion having larger ion radius than that of tetravalent cerium ion (Ce4+) and/or lower valence than Ce4+. As concrete examples of metal ions which can be used in this doping, Ca2+, Y3+, La3+, Nd3+, Eu3+, Tb3+, Sm3+, Mg2+, Sr2+, Ba2+, Ce3+ and the like can be mentioned. The desirable cerium oxide concentration in the metal oxide solid doped cerium oxide is 40 to 98 molar %. Further, when the color index of the metal oxide doped cerium oxide is estimated by L*, a* and b* values, the desirable region of L* is larger than 80, the desirable region of |a* | is smaller than 4, and desirable region of |b* | is smaller than 10. Preferably, the average particle size is ultra fine particle of 2 to 4 nanometers (nm).
Further the metal oxide doped cerium oxide of this invention can be prepared by following steps. That is, the metal oxide doped cerium oxide is formed at a temperature lower than 60xc2x0 C. and at a pH higher than 5 by reacting aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence than Ce4+ and alkali, then by adding oxidizing agent to the reaction mixture at the temperature lower than 60xc2x0 C. Furthermore the metal oxide doped cerium oxide of this invention can be prepared by adding and mixing aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence than Ce4+, alkali and oxidizing agent simultaneously at the temperature lower than 60xc2x0 C. at a pH higher than 5.
The present invention also relates to a composite composition of the metal oxide doped cerium oxide coated by one or more kinds of oxide selected from silicon oxide, zirconium oxide, aluminum oxide, iron oxide and titanium dioxide. Further, the present invention relates to a resin composition to which the metal oxide doped cerium oxide or the composite composition thereof is blended. Still further, the present invention relates to a cosmetic composition to which the metal oxide doped cerium oxide or the composite composition thereof is blended. The surface treated metal oxide doped cerium oxide or the composite composition thereof can be blended to the cosmetic composition. The cosmetic composition can also contain an ultraviolet ray absorbing agent and/or an ultraviolet ray scattering agent. As the desirable example of the ultraviolet ray absorbing agent, one or more kinds of compound selected from oxybenzone, octyl methoxycinnamate and 4-tert-butyl-4xe2x80x2-methoxy dibenzoylmethane can be mentioned, and the desirable content of the ultraviolet ray absorbing agent is 0.1 to 40% by weight. As the desirable example of the ultraviolet ray scattering agent, titanium dioxide and/or zinc oxide can be mentioned, and the desirable content of the ultraviolet ray scattering agent is 0.1 to 50% by weight. Above mentioned cosmetic composition is suited to be used as a sunscreen cosmetic composition.
The metal oxide doped cerium oxide of this invention is cerium oxide doped with metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+. By doping the metal ion, the catalytic activity of cerium oxide can be reduced. Further, by doping the metal ion, the transparency of cerium oxide is improved and the ultraviolet ray shielding effect can be improved. As concrete examples of metal ion which has larger ion radius than Ce4+ (ion radius of Ce4+ is 0.097 nm), Ca2+, La3+, Nd3+, Eu3+, Tb3+, Sm3+, and Ce3+ can be mentioned. As concrete examples of metal ion which has lower valence than Ce4+, Y3+, Mg2+, Sr2+ and Ba2+ can be mentioned in addition to the above mentioned metal ions. These metal ions can be used alone or together. In addition, the desirable concentration of metal oxide doped cerium oxide is 40 to 98 molar %.
The metal oxide doped cerium oxide of this invention can be prepared by the following steps. That is, metal hydroxide doped cerium hydroxide is prepared, for example, at a temperature lower than 60xc2x0 C. and in the condition of pH higher than 5, by reacting aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+ and alkali, then add oxidizing agent while maintaining the temperature lower than 60xc2x0 C. The obtained reacted product is rinsed with water, filtered, and dried or calcined, then pulverized. Thus, the metal oxide doped cerium oxide can be obtained. As concrete examples for the preparation of the solid solution of cerium hydroxide and metal hydroxide, the following methods can be mentioned. That is, (1) adding aqueous solution of cerium salt and aqueous solution of salt of metal to be dissolved, simultaneously into a container in which alkaline solution is contained, or (2) adding aqueous solution of cerium salt, alkaline solution and aqueous solution of salt of metal to be dissolved, simultaneously into a container in which water is contained.
Furthermore, the metal oxide doped cerium oxide of this invention can be prepared by adding and mixing aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+, alkali and oxidizing agent simultaneously. For instance, at the temperature lower than 60xc2x0 C. and in the condition of pH higher than 5, aqueous solution of cerium salt, aqueous solution of salt of metal to be dissolved, alkaline solution and hydrogen peroxide, which is an oxidizing agent, are added simultaneously into a container in which water is contained. The obtained reacted product is rinsed with water and filtered, dried or calcined then pulverized, thus the fine particles of metal oxide doped cerium oxide can be prepared.
Aqueous solution of cerium salt which is used in above mentioned reaction, can be prepared by dissolving, e.g. cerium carbonate, in aqueous solution of hydrochloric acid or nitric acid, or by dissolving cerium chloride, cerium nitrate, cerium sulfate or cerium acetate in water. As alkali, aqueous solution of alkali metal hydroxide, such as, sodium hydroxide or potassium hydroxide, or aqueous solution of ammonia, can be used. Further, as the salt of metal to be doped, for example, chloride, salt of nitric acid, salt of sulfuric acid or salt of acetic acid, can be mentioned. As the oxidizing agent, hydrogen peroxide, hypochlorous acid, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite and ozone can be used. In above mentioned methods, the doping is carried out in aqueous solution, however, the invention is not limited to these examples.
In any kind of above mentioned reacting method, nano-size particles of metal oxide doped cerium oxide having 2 to 4 nm average diameter can be obtained by keeping the temperature of solution lower than 60xc2x0 C., desirably lower than 40xc2x0 C. and by maintaining pH higher than 5 during the adding process of oxidizing agent. Such kind of fine pulverized particles of metal oxide doped cerium oxide have a superior transparency in the visible ray range and have an excellent dispersability, further, have a good ultraviolet ray shielding effect.
Further, in any kind of above mentioned reacting method, the yellowish tendency of metal oxide doped cerium oxide can be moderated so that white particles are obtained. And when the color index is estimated by L*, a* and b* space, the metal oxide doped cerium oxide whose L* is larger than 80, |a* | is smaller than 4, and |b* | is smaller than 10, can be obtained. In this invention, the term of L*, a* and b* space is regulated by CIE1976L* a* b* color space which is authorized by CIE (Commission Internationale de Enluminure) in 1976. This color space is a coordinate having axis of L*, a* and b* which are regulated by following numerical formulae.
L*=116(Y/Y0)1/3xe2x88x9216
a*=500[(X/X0)1/3xe2x88x92(Y/Y0)1/3]
b*=200[(Y/Y0)1/3xe2x88x92(Z/Z0)1/3]
(wherein, X/X0, Y/Y0, Z/Z0 greater than 0.008856, X,Y and Z indicate 3 stimulate values of object color, X0, Y0 and Z0 indicate 3 stimulate values of color source which illuminates the object, and standardized to Y0=100).
In the present invention, color index estimated by L*, a* and b* space is settled to L*xe2x89xa780, |a* |xe2x89xa64, |b* |xe2x89xa610. And each L*, a* and b* value are measured by color difference meter (product of Nihon Denshoku Kogyo).
The metal oxide doped cerium oxide of this invention can be used in the composite form, namely coated with oxide (hereinafter the composite may be referred to as xe2x80x9coxide coated metal oxide doped cerium oxidexe2x80x9d). As the oxide to be used for the preparation of the oxide coated metal oxide doped cerium oxide, one or more kinds of compound selected from silicon oxide, zirconium oxide, aluminum oxide, iron oxide and titanium dioxide, may be used. By the use of composite of metal oxide doped cerium oxide which is coated with oxide, the catalytic activity can be made weaker and the dispersability can be improved.
The oxide coated metal oxide doped cerium oxide can be prepared by the further treatment of metal oxide doped cerium oxide prepared by the use of aforementioned starting materials and by aforementioned method with oxide. For example, aqueous solution of cerium salt, aqueous solution of salt of metal to be doped (e.g. salt of calcium) and aqueous solution of alkali are added into water which is kept at the temperature lower than 60xc2x0 C. and higher than pH 9, then calcium hydroxide doped cerium hydroxide can be obtained. An oxidizing agent such as hydrogen peroxide is further added to generate calcium oxide doped cerium oxide. Then, the mixture is heated to a temperature higher than 80xc2x0 C. while keeping pH higher than 9, aqueous solution of sodium silicate and aqueous solution of mineral acid such as hydrochloric acid, nitric acid or sulfuric acid are added to coat silicon oxide over calcium oxide doped cerium oxide, and rinsed by water, filtered, dried, calcined and pulverized. Thus, silicon oxide coated calcium oxide doped cerium oxide can be obtained. In this case, desirable amount of sodium silicate to be added is 2 to 60% by weight to coat subject of solid solution as SiO2. Also in this case, by keeping pH of solution under 8 at the finishing point of oxidation, the yellowish tendency of oxide coated metal oxide doped cerium oxide can be weakened and improve the color index, and the metal oxide doped cerium oxide whose L* value is bigger than 80, absolute value of a* is smaller than 4 and absolute value of b* is smaller than 10 when color index is estimated by L* a* and b* space can be obtained. Further, by keeping pH of solution higher than 5 during oxidizing agent adding process, ultrafine particles of silicon oxide coated calcium oxide doped cerium oxide whose average particle diameter is 2 to 4 nm can be obtained.